Probe systems are employed to enable computer-controlled circuit testers to exercise various portions of circuitry contained within a device under test (DUT). A critical feature of a probe system is an ability to accurately position needle probes in contact with pads on the DUT, with sufficient contact pressure to assure a reliable electrical connection. In earliest probe systems, a probe card was set in place over a DUT in the view field of a stereo microscope. An operator observed the probe needle tips and controlled movable stages to bring both the DUT and probe needle tips into contact. Later wafer probe systems incorporated automatic needle tip/wafer alignment systems that employed image recognition cameras.
A probe system, in addition to assuring proper registration between probe tips and contact pads on a DUT, must control contact pressure between the contact pads and probe tips. If too little pressure is exerted, a high resistance connection may occur. If too much pressure is exerted, the wafer pad and/or probe tip may be damaged.
In U.S. Pat. No. 4,929,893 to Sato et al., a probe system is described which employs a piezoelectric touch plate to determine the height (i.e., along a Z axis) of a group of probe tips in relation to a DUT support. Sato et al. employ a plurality of cameras to image various aspects of the probe tips and a DUT to enable X,Y dimension registration therebetween. Such imaging occurs from cameras positioned at disparate locations within the probe system and requires precise knowledge of the relative locations of the cameras. The probe tips and DUT are moved into registration subsequent to imaging.
Such image recognition systems are also employed to assure registration of layers of a semiconductor wafer (see U.S. Pat. No. 4,938,600 to Into).
It is an object of this invention to provide an improved probe system which employs only the same electronically controllable, imaging system to view both a DUT and a set of probe needles.
It is another object of this invention to provide an improved probe system wherein plural imaging cameras employ the same objective lens.
It is yet another object of this invention to provide an improved probe system wherein positions of both a DUT and needle probes are determined by a single imaging apparatus that enables probe contact pressures to be precisely controlled.